The present invention relates generally to a variable pressure relief valve and more particularly to a single stage variable pressure relief valve that effectively controls flow forces acting thereon.
Variable pressure relief valves are well known. Many of them are two stage types that require a pilot stage valve that controls a main valving element. These types of pressure relief valves typically are larger, more expensive and require small orifices that may become plugged thus effecting the reliability of the pressure relief valve. Many of the known variable pressure relief valves are single stage relief valves that also require small bleed orifices that are subject to plugging and are also affected by flow forces acting to force the valving element open or closed depending on the structure of the valve. Many of the known variable pressure relief valves are electrically controlled in order to adjust the variability in pressure. Typically these electrical coils are large in size and very costly in order to provide the needed forces to offset the counteracting flow forces. One example of a typical two-stage variable pressure relief valve is set forth in U.S. Pat. No. 5,868,059 issued on Feb. 9, 1999 to David P. Smith who is also the inventor of the subject invention.
The subject invention is directed to overcome one or more of the problems set forth above.
In one aspect of the present invention a single stage, variable pressure relief valve assembly is provided and includes a housing, an electrically controlled coil assembly, a valving element assembly, a spring bumper plug and a spring member. The housing has a reference axis defined therein, a stepped bore defined therethrough along the reference axis, an inlet port, an outlet port and a bleed port in communication with the stepped bore. The stepped bore has a first diameter of a predetermined size and a second diameter of a larger predetermined size to established a differential area therebetween and the inlet and outlet ports open into the larger second diameter. The electrically controlled coil assembly has an armature disposed therein and is sealingly secured to the housing at one end of the stepped bore with the armature of the electrically controlled coil assembly being disposed generally parallel with the reference axis of the housing. The valving element assembly is slideably disposed in the stepped bore of the housing to define a fluid chamber between the valving element assembly and the electrically controlled coil assembly. The valving element assembly includes a sleeve member and a plug member. The sleeve member has first and second ends, a blind bore having a bottom, first and second ports, and a peripheral surface having first and second spaced apart peripheral lands. The first end of the sleeve member is in contact with the armature of the electrically controlled coil assembly. The blind bore in the sleeve member extends from the second end along the reference axis of the housing to the bottom thereof. The first peripheral land is spaced from the first end of the sleeve member and of a size to be slideably received within the first diameter of the housing and the second peripheral land is of a size to be slideably received in the larger second diameter of the housing to form a force control chamber therebetween. The first port of the sleeve member extend from the peripheral surface thereof to the blind bore and the second port thereof extends from the second peripheral land to the blind bore and both of the first and second ports are oriented generally perpendicular to the reference axis of the housing. The plug member has a bore defined therein and has first and second portions. The first portion has a diameter that extends into the blind bore and is sealingly secured to one end of the blind bore. The second portion of the plug member has a diameter larger than the diameter of the first portion thereof and is sealingly disposed in the blind bore of the sleeve member to define a flow control chamber between a portion of the blind bore of the sleeve member and the diameter of the first portion of the plug member. The flow control chamber extends parallel with the reference axis of the housing and is in continuous communication with the first and second ports of the sleeve member. A bleed control orificed passageway is disposed between the fluid chamber and the bore within the plug member. The spring bumper plug is secured in the stepped bore of the housing to form a spring chamber and located at the end thereof opposite to the electrically controlled coil assembly. The spring member is disposed in the valving element assembly between the sleeve member and the bumper plug and operative to urge the valving element assembly towards the electrically controlled coil assembly. The bleed port in the housing communicates with the spring chamber.